Project Summary/Abstract Parks are acknowledged as key elements of healthy communities. Proximity to and use of parks is associated with diverse health outcomes, including increased physical activity participation, reduced stress and morbidity, improved social capital, obesity prevention, and chronic disease mitigation. Despite these benefits and researchers' and planners' enthusiasm for park provision, it remains unclear which park metrics are most associated with park use. The heterogeneity in research on parks and health behaviors and outcomes impedes progress in the use of this evidence to inform public health practice and policy. The long-term goal of our research program is to increase the contribution of public parks to population health through improving their distribution, design, and use. The proposed study advances that agenda through the development of ParkIndex, a tool that incorporates elements related to park proximity, features, quality, and the surrounding neighborhood to allow researchers, planners, and citizens to evaluate the potential for park access and use for a given address or geographical area. Specifically, the two related aims of this proposal are: 1) To develop a prototype park use probability algorithm (ParkIndex) incorporating key park metrics using park exposure and park use data from a recent study, and 2) To further refine ParkIndex and assess its predictive value and external validity through a pilot study within four additional communities. To accomplish these aims, we will build on our team's vast prior knowledge and experience and a recent comprehensive literature review about park metrics associated with park use. We will then use the input of an advisory board of professionals with expertise in parks, planning, and community health, focus groups with citizens, and detailed data from a recent study of park exposure and use to develop a preliminary ParkIndex formula. This prototype will then be validated through a pilot study in four diverse communities via the collection of additional park access and use data and then disseminated broadly through our advisory board's wide network. This innovative project will combine diverse methods and data sources and the expertise and input of researchers, practitioners, and citizens to develop an evidence-based yet user-friendly tool that can better predict park use in communities. ParkIndex will have both practical and conceptual significance in that it can be used by researchers in diverse disciplines (e.g., to apply consistent, empirically-derived metrics of park access across studies) and by public health, parks and recreation, and urban design professionals as a scenario planning tool for encouraging greater population-level park use (e.g., to estimate the effects of adding a certain-sized park to a neighborhood or a sports field or restroom to an existing park). In future, ParkIndex can be customized to diverse user groups and will serve as an open source resource that can be implemented by any researcher, municipality, parks department, or public health division to understand park use probabilities, identify specific intervention points and strategies, and, in general, better facilitate greater environmental justice, park use, and community health.